Structure-Based Design of Human TLR8-Specific Agonists with Augmented Potency and Adjuvanticity.

Human Toll-like receptor 8 (hTLR8) is expressed in myeloid dendritic cells, monocytes, and monocyte-derived dendritic cells. Engagement by TLR8 agonists evokes a distinct cytokine profile which favors the development of type 1 helper T cells. Crystal structures of the ectodomain of hTLR8 cocrystallized with two regioisomers of a dual TLR7/8-agonistic N1-substituted imidazoquinolines showed subtle differences in their interactions in the binding site of hTLR8. We hypothesized that the potency of a previously reported best-in-class pure TLR8 agonist, 3-pentylquinoline-2-amine, could be further enhanced by "designing in" functional groups that would mimic key intermolecular interactions that we had observed in the crystal structures. We performed a focused exploration of decorating the quinoline core with alkylamino groups at all possible positions. These studies have led to the identification of a novel TLR8 agonist that was ∼ 20-fold more potent than the parent compound and displays prominent adjuvantic activity in a rabbit model of immunization.

Introduction

The Centers for Disease Control and Prevention (CDC) has declared vaccination and the control of infectious diseases to be among the greatest public health achievements of the 20th century.[1] Vaccines afford protection by the induction of immune responses, both humoral and cellular, specifically directed against the pathogen. A significant trend in contemporary vaccinology is the design of highly effective subunit vaccines, and the majority of modern subunit vaccines that utilize highly purified, recombinantly expressed protein immunogens are reliant on vaccine adjuvants[2,3] (substances that enhance immune responses) to provide the initial, innate immune-activating signals that determine the specificity, magnitude, quality, and durability of downstream adaptive immune responses.

With few exceptions, the majority of currently available vaccines contain a single adjuvant: “alum” introduced by Alexander Glenny in 1926.[4] “Alum” (a mixture of aluminum phosphate and aluminum hydroxide) appears to promote a T helper 2 (Th2) skewed antibody response.[5,6] Indeed, alum-adjuvanted pertussis subunit vaccines,[7] which supplanted killed whole-cell pertussis vaccines in the 1990s, induce immunity that rapidly wanes;[8−10] the short-lived immunity is thought to contribute to the recent re-emergence of pertussis in the United States[11,12] and elsewhere in the world.[13,14] In experimental models of pertussis, alum-adjuvanted acellular pertussis vaccines protected baboons in the short term from severe pertussis-like symptoms but failed to prevent colonization of B. pertussis, allowing transmission of the pathogen to unvaccinated animals;[15] killed whole-cell pertussis vaccines, on the other hand, elicited strong B. pertussis-specific Th17 and Th1 memory,[15] indicating that both durability and quality of immune responses are pivotal in the induction and maintenance of long-term sterilizing immunity.

Innate immune signals evoked by vaccine adjuvants include those originating from Toll-like receptors (TLRs),[16−18] as well as RIG-I-like receptors[19] and NOD-like receptors (NLRs).[20,21] There are 10 functional TLRs encoded in the human genome, which are transmembrane proteins with an extracellular domain having leucine-rich repeats (LRR) and a cytosolic domain called the Toll/IL-1 receptor (TIR) domain.[17] The ligands for these receptors are highly conserved molecules such as lipopolysaccharides (LPS) (recognized by TLR4), lipopeptides (TLR2 in combination with TLR1 or TLR6), flagellin (TLR5), single stranded RNA (TLR7 and TLR8), double stranded RNA (TLR3), CpG motif-containing DNA (recognized by TLR9), and profilin present on uropathogenic bacteria (TLR11).[17] TLR1, -2, -4, -5, and -6 recognize extracellular stimuli, while TLR3, -7, -8, and -9 function within the endolysosomal compartment.

Our understanding of how the engagement of innate immune receptors by vaccine adjuvants leads to the deployment and amplification of immunogen-specific adaptive immune responses,[16,17,22] and the maintenance of immunological memory is incomplete and may involve multiple mechanisms and pathways; these may include (i) enhanced antigen uptake and presentation by professional antigen presenting cells (APCs),[23−30] (ii) amplification of cross-talk[31−33] between naive B lymphocytes recognizing the immunogen and rare naive CD4+ T cells expressing T cell antigen receptors (TCRs) specific for antigen-derived peptide/major histocompatibility complex class II molecules (MHCII) displayed by such naive B cells, (iii) accelerated differentiation of CD4+ T cells into follicular helper T cells (Tfh),[34−37] and (iv) subsequent B lymphocyte differentiation events leading to immunologulin affinity maturation[38,39] and the generation of antigen-specific memory B cells and plasma cells.[40−42]

The need for the development of safe and effective vaccine adjuvants has fueled our exploration of a variety of innate immune stimuli, which include agonists of TLR2,[43−45] TLR7,[46−54] TLR8,[54−59] nucleotide oligomerization domain 1 (NOD1),[60] as well as C–C chemokine receptor type 1 (CCR1).[61] Structure–activity relationship studies have proven useful in providing tools with which to examine how these different classes of innate immune signaling molecules affect and modulate pathways linking the innate and adaptive immune systems described above.

TLR8 is expressed predominantly in myeloid dendritic cells, monocytes, and monocyte-derived dendritic cells.[62,63] Engagement by TLR8 agonists evokes a dominant proinflammatory cytokine profile, including tumor necrosis factor α (TNF-α), interleukin (IL)-12, and IL-18 and appear uniquely potent in enhancing the production of Th1-polarizing cytokines TNF-α and IL-12 in APCs.[62,64−66] Our interest in small molecule agonists of TLR8 has led to the exploration of the 2,3-diaminofuro[2,3-c]pyridines,[55] 4-aminofuro[2,3-c]quinolines,[57] 3-alkylquinoline-2-amines,[58] and 1-alkyl-2-aminobenzimidazoles,[59] all of which are pure TLR8 agonists with no detectable activity at TLR7.

Crystal structures of the ectodomain of human TLR8 (hTLR8) cocrystallized with two regioisomers of dual TLR7/8-agonistic N1-aminomethylbenzyl-substituted imidazoquinolines[47] (1, 2) showed subtle differences in their interactions in the binding site of hTLR8 (Figure ). The N1-substituent of 1 was observed to H-bond with a backbone carbonyl group, while in 2, a stronger salt-bridge was present, which fully explained the higher TLR8 activity of 2. We sought to apply these findings and asked whether the TLR8-agonistic potency of the best-in-class compound of the 3-alkylquinoline-2-amine series[58] could be further enhanced by “designing in” functional groups which would mimic the ionic H-bond observed in the hTLR8/2 complex. We now report a focused and hypothesis-driven exploration of introducing alkylamino groups at all possible positions on the quinoline core. These studies led to the identification of a novel TLR8 agonist which was ∼20-fold more potent than the parent compound.

Figure 1

Left: structures of the dual TLR7/8-active N1-4-aminomethylbenzyl (1) and N1-3-aminomethylbenzyl (2) substituted imidazoquinolines and pure TLR8-agonistic 3-pentylquinolin-2-amine (3). Right: Crystal structures of 1 and 2 bound to human TLR8. Dashed lines in yellow depict direct hydrogen bonds.

Results and Discussion

The dual TLR7/8-active regioisomeric imidazoquinolines 1 and 2 (Figure ), synthesized when we first began our investigations on TLR-active compounds,[47] showed substantially different agonistic potencies in human TLR7 (1, 50 nM; 2, 215 nM) and TLR8 (1, 55 nM; 2, 14 nM) primary screens (Figure S1 in Supporting Information). The crystal structures of these two congeners bound to the ectodomain of human TLR8 reveal the structural basis of enhanced TLR8-agonistic potency of 2 relative to 1: the 3-aminomethylbenzyl substituent in 2 forms a strong ionic H-bond (salt bridge) with the side chain carboxylate of Asp545, while the 4-aminomethylbenzyl substituent in 1 is observed to engage the backbone carbonyl of Gly351 in a weaker H-bond (Figure ). The stronger interaction of 2 in its binding site resulted not only in enhancement of agonistic activity in primary screens (Figure S1) but also in higher proinflammatory cytokine induction in whole human blood assays (data not shown). The 3-pentylquinoline-2-amine 3, derived from structure-based ligand design, had previously been identified as a human TLR8-specific agonist (EC50 = 200 nM).[58]

We asked whether grafting the aminomethylbenzyl group on to the 3-pentylquinoline-2-amine moiety would result in augmented activity. Direct SNAr displacement of the 4-chloro-3-(pent-1-yn-1-yl)quinoline intermediate[58]4 with 3- or 4-cyanobenzylzinc bromide as nucleophile[67] afforded the 4-substituted 3-pentynylquinolines 5a and 5b (Scheme ); reduction of the nitriles with LiAlH4 and subsequent Boc protection of the resultant amines yielded the intermediates 6a and 6b. Installation of the amine at C2 was performed as reported earlier.[58] Hydrogenation of the alkynyl group and Boc-deprotection furnished the desired target compounds 9a and 9b (Scheme ) which retained specificity for TLR8 but with marginal improvement in potency (150 and 120 nM, respectively; Table ). In order to examine relieving possible steric bulk of the aminomethylbenzyl substituent at C4, we undertook the synthesis of the 4-aminobutyl (14a) and 5-aminopentyl (14b) analogues (Scheme ), the lengths of which were found to be optimal in SAR studies on several TLR8-active chemotypes.[54,55,57−59] Installation of the 4-alkylnitrile groups of 10a,b was carried out with cyanoalkylzinc bromides under Negishi conditions (Scheme ), and the remainder of the sequence of reactions was similar to those described in Scheme . The potencies of 14a and 14b remained virtually unchanged (190 and 250 nM, respectively; Table ).

Scheme 1

Reagents: (i) 3-cyanobenzylzinc bromide (for 5a) or 4-cyanobenzylzinc bromide (for 5b), LiCI, DMF; (ii) (a) LiAIH4, THF, (b) Boc2O, CH3OH; (iii) m-CPBA, CHCl3; (iv) (a) benzoyl isocyanate, CH2CI2, (b) NaOCH3, CH3OH; (v) (a) Pt/C, EtOAc, 30 psi, (b) HCI, 4 M.

Table 1

EC50 Values of Compounds in Human TLR8-Specific Reporter Gene Assays

EC50 values represent the arithmetic mean values obtained on quadruplicate samples.

Scheme 2

Reagents: (i) 3-cyanopropylzinc bromide (for 10a) or 4-cyanobutylzinc bromide (for 10b), Pd(PPh3)4, THF; (ii) (a) LiAlH4, THF, (b) Boc2O, CH3OH; (iii) m-CPBA, CHCl3; (iv) (a) benzoyl isocyanate, CH2CI2, (b) NaOCH3, CH3OH; (v) (a) Pt/C, EtOAc, 30 psi, (b) HCI, 4 M.

Our first attempts at attaching amine-bearing appendages on the quinoline core at C4 to allow for additional salt-bridge interactions with Asp545 appeared unfruitful, and we set out to systematically examine substitutions at all other positions. We desired an efficient synthetic strategy to access 5-, 6-, 7-, and 8-substituted 2-amino-3-pentylquinolines. A one-pot method for the syntheses of 2-aminoquinoline-3-carboxamides has been reported using 2-aminobenzaldehyde and active methylene-group-bearing cyanoacetamides.[68] We envisioned that a modified Friedländer synthesis of key bromo-substituted 2-amino-3-pentylquinolines could be directly obtained via condensation–cyclization reactions of 2-aminobromobenzaldehydes with heptanenitrile. Our initial attempts at model reactions with alkane nitriles and the unsubstituted 2-aminobenzaldehyde proceeded very well in the presence of n-butyllithium. However, in order to preempt possible debromination, we sought alternatives and successfully utilized potassium tert-butoxide to generate the pivotal bromo-substituted 2-amino-3-pentylquinolines (Schemes –7).

Scheme 3

Reagents: (i) heptanenitrile, t-BuOK, DMSO; (ii) 3-cyanobenzylzinc bromide (for 17a) or 4-cyanobenzylzinc bromide (for 17b) or 2-cyanobenzylzinc bromide (for 17c) or benzylzinc bromide (for 17d), Pd(PPh3)4, THF; (iii) LiAIH4, THF; (iv) KOH, t-BuOH, 8 h.

Scheme 7

Reagents: (i) LiAIH4, THF; (ii) MnO2, DCM; (iii) heptanenitrile, t-BuOK, DMSO; (iv) 4-cyanobutylzinc bromide, Pd(PPh3)4, THF; (v) LiAIH4, THF, 4 h.

We targeted 2-amino-3-pentylquinolines substituted at C5 with 3-aminomethylbenzyl (18a), 4-aminomethylbenzyl (18b), and 2-aminomethylbenzyl (18c) substituents, which were obtained by Negishi coupling of corresponding cyanobenzylzinc bromides with 16 (Scheme ). Substantially improved potencies were observed for both 18a and 18b (EC50 of 49 and 38 nM, respectively; Figure , Table ), whereas the 2-aminomethylbenzyl-substituted 18c was significantly weaker (EC50 = 1000 nM; Table ) than the parent compound, 3, suggesting that the placement of the amine on the benzyl substituent was an important determinant of activity. In order to formally test whether the amine was participating in the predicted salt bridge, the nitrile 17a was hydrolyzed to the carboxamide analogue 18d (Scheme ). Compound 18d and the 5-benzyl analogue 17d were found to be inactive (Table ), lending support to our hypothesis.

Figure 2

Agonistic activities of analogues 18a, 18b, 34a, and 34b in human TLR8 reporter gene assays. Mean values ± SD on quadruplicates are shown. Also included is 3, used as a reference/comparator compound.

We next explored the role of conformational flexibility of the aminomethylbenzyl substituent at C5, and we therefore synthesized the aryl–aryl coupled 5-(aminomethyl)phenyl analogues 20a and 20b via Suzuki reaction of cyanophenylboronic acids with 16 (Scheme ). Compound 20a was entirely inactive, and the activity of 20b was attenuated (699 nM), strongly pointing to the indispensability of conformational freedom. These findings prompted us to synthesize 5-aminoalkyl analogues (Schemes and 6). The aminobutyl (34a), aminopentyl (34b), and aminohexyl (34c) derivatives could be accessed via Negishi couplings (Scheme ); the reactivity of 2-cyanoethylzinc bromide with 16, however, was very poor even under microwave conditions, and the aminopropyl analogue 23 was accessed via Heck reaction of acrylonitrile with 16 (Scheme ). A clear dependence on the length of the alkylamine substituent was observed in these homologues with progressive increases in potency from the aminopropyl (23, 91 nM), aminobutyl (34a, 27 nM; Figure ) and aminopentyl (34b, 9 nM; Figure ) analogues; a further increase in length (34c, aminohexyl) led to decreased activity (56 nM, Table ). Conversion of the nitrile precursor 30a to the carboxamide derivative 34d (Scheme ) resulted in a dramatic decrease in potency (2181 nM, Table ), once again highlighting the importance of the presence of a free amino functional group.

Scheme 4

Reagents:(i) 3-cyanophenylboronic acid (for 19a) or 4-cyanophenylboronic acid (for 19b), Pd(dppf)C12, K2CO3, 1,4-dioxane; (ii) LiAIH4, THF, 5 h.

Scheme 5

Reagents: (i) acrylonitrile, Pd(OAc)2, PPh3, K2CO3, DMF; (ii) H2, Pt/C, 30 psi, EtOAc; (iii) LiAIH4, THF.

Scheme 6

Reagents: (i) heptanenitrile, t-BuOK, DMSO; (ii) 3-cyanopropylzinc bromide (for 30a–32a and 33) or 4-cyanobutylzinc bromide (for 30b–32b) or 5-cyanopentylzinc bromide (for 30c–32c), Pd(PPh3)4, THF; (iii) LiAIH4, THF; (iv) KOH, t-BuOH, 8 h; (v) 1H-pyrazole-1-carboxamidine HCI, Et3N, MeOH.

The dramatic enhancement of potency in 34b seemed to unambiguously support our hypothesis of a salt-bridge between Asp545 and the 5-aminopentyl group of the lead compound. Given that guanidine–carboxylate interaction in proteins are consequential[69,70] and significant gains in interaction energies are observed in drugs such as zanamivir and peramivir whose crystal structures show strong salt-bridges between their guanidinium functional groups and the Asp/Glu residues that they interact with,[71] we synthesized from 34a the guanidine derivative 34e (Scheme ), the length of the C5 substituent of which was calculated to be comparable to that of 34b. We found, to our surprise, a precipitous fall in activity (2862 nM, Table ), the reasons for which are yet to be understood.

We also explored aminoalkyl substitutions at C6 (35a–c), C7 (36a–c), and C8 (37) (Scheme ). Compounds 35a–c showed slight decreases in activity while analogues 36a–c displayed modest gains in potency, with the most active compound being the 7-(5-aminopentyl)-3-pentylquinolin-2-amine, 36b (50 nM). The C8-substituted analogue 37 was entirely devoid of activity (Table ). Noting that the most potent analogues possessed an aminopentyl substituent either at C5 (34b, 9 nM) or C7 (36b, 50 nM), we wished to synthesize a dually substituted analogue. The key precursor 2-amino-4,6-dibromobenzaldehyde was synthesized from 2-amino-4,6-dibromobenzoic acid using conventional methods, and alkylamino substituents at C5 and C7 installed via Negishi reaction of 41 with 4-cyanobutylzinc bromide (Scheme ). The disubstituted analogue 43, however, was found to be weaker (621 nM) than the parent compound.

The most potent analogue 34b was characterized further in cytokine/chemokine induction profiles in a panel of secondary screens employing human peripheral blood mononuclear cells as well as whole human blood. Consistent with its specificity and potency for TLR8, we observed not only the induction of a specific set of proinflammatory cytokines, including TNF-α, IL-12, and IFN-γ (Figure ), but also that the potency of 34b was significantly higher than that of both 3 (TLR8-specific) and 1 (dual TLR7/8-active). As observed in our previous studies, these agonists also induce responses which are distinctly biphasic, with higher concentrations of ligand leading to an apparent suppression of cytokine production (Figure ). None of the active compounds displayed any detectable cytotoxicity at concentrations up to 100 μg/mL, and the origin of the apparent suppression of responses is presumed to be due to large excesses of ligand disfavoring dimerization of TLR8.

Figure 3

Representative cytokine induction data (excerpted from a 63 cytokine panel) in human PBMCs. Mean values ± SD on quadruplicates are shown.

We compared the adjuvantic activity of 34b (TLR8 EC50 = 9 nM) with that of 3 (200 nM), as well as a first-generation C2-butylfuro[2,3-c]quinoline[57] (1600 nM) in a rabbit model of immunization, using the diphtheria toxin mutein CRM197[72] as a model antigen. CRM197 has served as a carrier protein for conjugate vaccines against encapsulated bacteria such as Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis. We observed a clear dependence between antigen-specific IgG titers and TLR8-agonistic potency (Figure ).

Figure 4

Adjuvanticity of TLR8-active compounds. Cohorts of adult female New Zealand white rabbits (n = 4) were immunized intramuscularly in the flank region with (a) 10 μg of CRM197 in 0.2 mL of saline (unadjuvanted control) or (b) 10 μg of CRM197 in 0.2 mL of saline plus 100 μg of lead TLR8 agonists (3, 34b, and a TLR8-specific furoquinoline agonist[57]). Preimmune test-bleeds were obtained on day 0, and animals were immunized on days 1, 15, and 28. A final bleed was obtained on day 38. CRM197-specific ELISAs were performed using automated liquid handling methods and are depicted as log10 (immune/preimmune) titers.

An aspect of our work on vaccine adjuvant discovery, in addition to elucidating of structure–activity relationships in lead candidate vaccine adjuvants, is to delineate specific mechanisms by which these compounds elicit adjuvantic effects. As alluded to earlier, our understanding of how efferent signals arising from activation of the innate immune system engage particular pathways in downstream adaptive immune responses culminating, for instance, in the generation of antigen-specific humoral responses is nascent and fragmentary. One of the questions that we have begun to address is how various chemotypes acting on different innate immune receptors with divergent outcomes effect enhancement of immune responses. Pure TLR8 agonists, as discussed earlier, evoke the production of Th1-biased cytokines such as TNF-α, IL-1, IL-12, IL-18, and IFN-γ from cells of the monocytoid lineage; pure TLR7-active compounds induce the copious production of IFN-α from low-abundance plasmacytoid cells, activate natural killer (NK),[73] and induce mitogenicity in B lymphocytes (manuscript in preparation) and are much weaker in inducing TNF-α and IFN-γ; TLR2 agonists, in contrast, activate neutrophils as evidenced by rapid upregulation of CD11b and p38 MAP kinase activity.[43,44] The observation that all these chemotypes display adjuvantic activities may signify that the disparate outcomes in different cell types may point to different mechanisms mediating adjuvantic activities such as, as discussed earlier, enhanced antigen uptake and presentation by APCs,[23−30] enhanced CD4+ T helper cell activation,[31−33] or affinity maturation of antibodies.[38,39]

In an attempt to understand how TLR8 agonism may modulate adaptive immune functions, we used eight-color flow cytometry to interrogate activation markers (CD40, CD80) in major cellular subsets (granulocytes, monocytes (CD14+), T cells (CD3+), B cells (CD19+), NK cells (CD3–CD56+), and cytokine-induced killer cells (CD3+CD56+) in human whole blood stimulated with 34b, the significantly weaker TLR8-specific 3, as well as the potent, dual TLR7/8-active 1; we found that whereas both 34b and 1 upregulate CD40, specifically in CD14+ monocytes (and not in other subsets), the TLR8 stimulation with 34b strongly induces CD80 expression in the monocytes (Figure ), and in these assays, differences in potency between 34b and 1 become readily evident (Figure ). These results hint at a possible specific role of TLR8 agonists at enhancing antigen presentation and point a way forward to exploring this phenomenon in greater detail.

Figure 5

Eight-color flow cytometry. Top: gating strategy for identification of B, T, NK lymphocytes, monocytes, and granulocytes. Monocytes were identified directly based on CD14+ phenotype. Lymphocytic subsets were identified based on CD3, CD19, CD56 staining patterns as described in the Experimental Section. Bottom: stimulation of whole human blood TLR8-active compounds leading to upregulation of CD40 and CD80 in CD14+ monocytes, denoted by increase in mean fluorescence intensity (MFI).

In conclusion, our hypothesis-driven approach of augmenting potency by exploiting key interactions identified in crystallographic studies of TLR8 has yielded novel analogues of extraordinary potency and specificity which are proving useful in understanding the immunological basis of adjuvanticity in this chemotype.

Experimental Section

Chemistry

All of the solvents and reagents used were obtained commercially and used as such unless noted otherwise. Moisture- or air-sensitive reactions were conducted under nitrogen atmosphere in oven-dried (120 °C) glass apparatus. Solvents were removed under reduced pressure using standard rotary evaporators. Flash column chromatography was carried out using RediSep Rf “Gold” high performance silica columns on CombiFlash R instruments unless otherwise mentioned, while thin-layer chromatography was carried out on silica gel CCM precoated aluminum sheets. Purity for all final compounds was confirmed to be greater than 98% by LC–MS using a Zorbax Eclipse Plus 4.6 mm × 150 mm, 5 μm analytical reverse phase C18 column with H2O–CH3CN and H2O–MeOH gradients and an Agilent 6520 ESI-QTOF accurate mass spectrometer (mass accuracy of 5 ppm) operating in the positive ion acquisition mode. Compound 4 was synthesized as published by us earlier.[58]

3-((3-(Pent-1-yn-1-yl)quinolin-4-yl)methyl)benzonitrile (5a)

To a solution of compound 4 (230 mg, 1 mmol) in DMF (5 mL) were added 3-cyanobenzylzinc bromide (4 mL, 2 mmol, 0.5 M in THF) and LiCl (85 mg, 2 mmol). The resulting reaction mixture was stirred for 24 h at room temperature under nitrogen atmosphere. The reaction mixture was diluted with water and extracted with EtOAc (3 × 30 mL). The combined organic layer was dried over Na2SO4 and concentrated under reduced pressure. The crude material was purified by flash chromatography (40% EtOAc/hexanes) to obtain the compound 5a as a pale yellow solid (179 mg, 58%). 1H NMR (500 MHz, CDCl3) δ 8.93 (s, 1H), 8.10 (dd, J = 1.2, 8.4 Hz, 1H), 7.87 (dd, J = 1.3, 8.3 Hz, 1H), 7.67 (ddd, J = 1.3, 6.9, 8.4 Hz, 1H), 7.55–7.50 (m, 2H), 7.49–7.46 (m, 1H), 7.44–7.41 (m, 1H), 7.34 (t, J = 7.7 Hz, 1H), 4.65 (s, 2H), 2.47 (t, J = 7.0 Hz, 2H), 1.73–1.52 (m, 2H), 1.02 (t, J = 7.4 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 152.89, 147.08, 145.67, 140.55, 132.90, 132.02, 130.52, 130.36, 129.55, 129.51, 127.65, 126.62, 123.91, 119.01, 118.90, 112.77, 98.31, 77.53, 35.56, 22.20, 21.80, 13.70. MS (ESI-TOF) for C22H18N2 [M + H]+ calculated 311.1543, found 311.1441.

4-((3-(Pent-1-yn-1-yl)quinolin-4-yl)methyl)benzonitrile (5b)

Compound 5b was synthesized similarly as compound 5a. 4-Cyanobenzylzinc bromide was used as reagent. Pale yellow solid (201 mg, 65%). 1H NMR (500 MHz, CDCl3) δ 8.93 (s, 1H), 8.09 (dd, J = 0.8, 8.4 Hz, 1H), 7.84 (dd, J = 0.8, 8.5 Hz, 1H), 7.67 (ddd, J = 1.4, 6.9, 8.4 Hz, 1H), 7.56–7.48 (m, 3H), 7.32–7.26 (m, 2H), 4.69 (s, 2H), 2.46 (t, J = 7.0 Hz, 2H), 1.74–1.51 (m, 2H), 1.01 (t, J = 7.4 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 152.87, 147.07, 145.59, 144.64, 132.54, 130.50, 129.55, 129.18, 127.61, 126.68, 123.97, 119.08, 118.94, 110.49, 98.24, 77.50, 36.17, 22.19, 21.79, 13.69. MS (ESI-TOF) for C22H18N2 [M + H]+ calculated 311.1543, found 311.1504.

4-(3-(Aminomethyl)benzyl)-3-pentylquinolin-2-amine Dihydrochloride (9a)

A solution of compound 5a (155 mg, 0.5 mmol) in THF (5 mL) was added slowly to a solution of LiAlH4 (2.5 mL, 2.5 mmol, 1.0 M in THF) in THF (5 mL) at 0 °C under nitrogen atmosphere. The reaction mixture was stirred for 1 h at 25 °C and 5 h at 75 °C. The reaction mixture was cooled to room temperature and quenched carefully with ice-cold water. The resulting mixture was basified with 10% NaOH (to pH = 8.0) and extracted with CH2Cl2 (3 × 30 mL). The combined organic layer was dried over Na2SO4 and concentrated under reduced pressure to obtain the residue. The residue was dissolved in MeOH, and di-tert-butyl dicarbamate (109 mg, 0.5 mmol) was added and stirred under nitrogen for 1 h. The solvent was removed under vacuum. The resulting residue was purified by flash chromatography (20% EtOAc/hexanes) to obtain the compound 6a as a pale yellow solid (134 mg, 65%). MS (ESI-TOF) for C27H30N2O2 [M + H]+ calculated 415.2380, found 415.2266. To a stirred solution of substrate 6a (124 mg, 0.3 mmol) in CHCl3 was added m-CPBA (134 mg, 0.6 mmol). The resulting reaction mixture was stirred for 4 h at room temperature. The reaction mixture was diluted with water and extracted with CH2Cl2 (3 × 20 mL). The combined organic layer was dried over Na2SO, concentrated under reduced pressure, and the crude material was purified by flash chromatography (10% MeOH/CH2Cl2) to obtain 7a as a yellow solid (98 mg, 76%). MS (ESI-TOF) for C27H30N2O3 [M + H]+ calculated 431.2329, found 431.2122. To a stirred solution of 7a (86 mg, 0.2 mmol) in CH2Cl2 was added benzoyl isocyanate (88 mg, 0.6 mmol). The resulting reaction mixture was stirred at 55 °C for 1 h. After completion of reaction (monitored by TLC), the solvent was removed under reduced pressure. The residue was redissolved in MeOH (5 mL), and NaOMe (54 mg, 1 mmol) was added and refluxed for 2 h. The solvent was removed and the crude material was purified by flash chromatography (10% MeOH/CH2Cl2) to obtain 8a as a off-white solid (67 mg, 78%). MS (ESI-TOF) for C27H31N3O2 [M + H]+ calculated 430.2489, found 430.2303. To a solution of compound 8a (43 mg, 0.1 mmol) in anhydrous EtOAc (10 mL) was added a catalytic amount of Pt/C, and the reaction mixture was subjected to hydrogenation at 30 psi for 30 min. The reaction mixture was filtered and the filtrate concentrated under reduced pressure. The crude material was purified by flash chromatography (10% MeOH/CH2Cl2) to obtain N-Boc protected benzylamine as a white solid (32 mg). MS (ESI-TOF) for C27H35N3O2 [M + H]+ calculated 434.2802, found 434.2612. To a stirred solution of N-Boc protected benzylamine (32 mg) in 1,4-dioxane (1 mL) was added hydrogen chloride (1 mL, 4 M in dioxane), and the reaction mixture was stirred for 1 h at room temperature. Excess solvent was removed under reduced pressure and the resulting residue was thoroughly washed with diethyl ether to obtain the desired compound 9a as a white solid (28 mg, 69%). 1H NMR (500 MHz, MeOD) δ 7.97–7.91 (m, 1H), 7.77–7.64 (m, 2H), 7.43 (ddd, J = 1.4, 7.0, 8.4 Hz, 1H), 7.38 (t, J = 7.6 Hz, 1H), 7.36–7.31 (m, 1H), 7.28 (s, 1H), 7.18 (d, J = 8.0 Hz, 1H), 4.62 (s, 2H), 4.06 (s, 2H), 2.81 (t, J = 8.5 Hz, 2H), 1.58–1.49 (m, 2H), 1.47–1.39 (m, 2H), 1.36–1.25 (m, 2H), 0.89 (t, J = 7.3 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 155.07, 151.34, 140.27, 136.23, 135.28, 133.06, 130.87, 129.87, 129.62, 128.43, 127.13, 126.67, 126.32, 123.05, 118.59, 44.08, 34.87, 32.75, 29.22, 28.11, 23.67, 14.34. MS (ESI-TOF) for C22H27N3 [M + H]+ calculated 334.2278, found 334.2238.

4-(4-(Aminomethyl)benzyl)-3-pentylquinolin-2-amine Dihydrochloride (9b)

Compound 9b was synthesized similarly as compound 9a. White solid (30 mg, 74%). 1H NMR (500 MHz, MeOD) δ 7.91 (dd, J = 1.2, 8.4 Hz, 1H), 7.79–7.64 (m, 2H), 7.44–7.37 (m, 3H), 7.22 (d, J = 8.0 Hz, 2H), 4.62 (s, 2H), 4.07 (s, 2H), 2.79 (t, J = 8.2 Hz, 2H), 1.57–1.47 (m, 2H), 1.46–1.38 (m, 2H), 1.36–1.27 (m, 2H), 0.89 (t, J = 7.3 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 155.04, 151.56, 140.37, 136.15, 133.09, 133.07, 130.67, 129.85, 127.14, 126.60, 126.20, 123.00, 118.56, 43.87, 34.72, 32.71, 29.19, 27.99, 23.62, 14.33. MS (ESI-TOF) for C22H27N3 [M + H]+ calculated 334.2278, found 334.2257.

4-(3-(Pent-1-yn-1-yl)quinolin-4-yl)butanenitrile (10a)

To a solution of compound 4 (229.7 mg, 1 mmol) in THF (4 mL) were added 3-cyanopropylzinc bromide (4 mL, 2 mmol, 0.5 M in THF) and Pd(PPh3)4 (115.5 mg, 0.1 mmol). The resulting reaction mixture was stirred for 12 h at 65 °C under nitrogen atmosphere. The reaction mixture was diluted with water and extracted with EtOAc (3 × 30 mL). The combined organic layer was dried over Na2SO4 and concentrated under reduced pressure. The crude material was purified by flash chromatography (20% EtOAc/hexanes) to obtain the compound 10a as a pale yellow oil (144 mg, 55%). 1H NMR (500 MHz, CDCl3) δ 8.84 (s, 1H), 8.11–8.06 (m, 1H), 7.98 (dd, J = 1.0, 8.9 Hz, 1H), 7.69 (ddd, J = 1.3, 6.8, 8.3 Hz, 1H), 7.59 (ddd, J = 1.3, 6.8, 8.3 Hz, 1H), 3.42 (t, J = 7.7 Hz, 2H), 2.53 (t, J = 7.0 Hz, 2H), 2.46 (t, J = 7.0 Hz, 2H), 2.14–2.03 (m, 2H), 1.77–1.62 (m, 2H), 1.10 (t, J = 7.4 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 152.74, 147.14, 146.93, 130.56, 129.49, 127.51, 126.37, 123.25, 119.48, 118.15, 98.32, 77.10, 28.90, 25.79, 22.27, 21.83, 17.31, 13.81. MS (ESI-TOF) for C18H18N2 [M + H]+ calculated 263.1543, found 263.1437.

5-(3-(Pent-1-yn-1-yl)quinolin-4-yl)pentanenitrile (10b)

Compound 10b was synthesized similarly as compound 10a. 4-Cyanobutylzinc bromide was used as reagent. Pale yellow oil (174 mg, 63%). 1H NMR (500 MHz, CDCl3) δ 8.83 (s, 1H), 8.07 (dd, J = 0.8, 8.5 Hz, 1H), 7.97 (dd, J = 1.0, 8.5 Hz, 1H), 7.67 (ddd, J = 1.4, 6.9, 8.3 Hz, 1H), 7.57 (ddd, J = 1.3, 6.9, 8.3 Hz, 1H), 3.30 (t, J = 7.5 Hz, 2H), 2.51 (t, J = 7.0 Hz, 2H), 2.40 (t, J = 7.0 Hz, 2H), 1.95–1.84 (m, 2H), 1.85–1.75 (m, 2H), 1.76–1.65 (m, 2H), 1.10 (t, J = 7.4 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 152.78, 148.54, 146.91, 130.45, 129.34, 127.22, 126.48, 123.54, 119.52, 117.88, 97.62, 77.51, 29.32, 29.02, 25.41, 22.33, 21.81, 17.20, 13.79. MS (ESI-TOF) for C19H20N2 [M + H]+ calculated 277.1699, found 277.1581.

4-(4-Aminobutyl)-3-pentylquinolin-2-amine Dihydrochloride (14a)

Compound 14a was synthesized similarly as compound 9a. White solid (28 mg, 78%). 1H NMR (500 MHz, MeOD) δ 8.11 (d, J = 8.1 Hz, 1H), 7.76 (ddd, J = 1.2, 7.1, 8.4 Hz, 1H), 7.67 (dd, J = 1.2, 8.4 Hz, 1H), 7.57 (ddd, J = 1.2, 7.1, 8.3 Hz, 1H), 3.19 (t, J = 8.2 Hz, 2H), 3.01 (t, J = 7.6 Hz, 2H), 2.80 (t, J = 8.2 Hz, 2H), 1.98–1.87 (m, 2H), 1.80–1.70 (m, 2H), 1.65–1.55 (m, 2H), 1.56–1.46 (m, 2H), 1.47–1.38 (m, 2H), 0.96 (t, J = 7.2 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 154.80, 154.01, 135.98, 133.05, 126.77, 126.45, 124.51, 122.47, 118.61, 40.50, 32.81, 29.52, 29.45, 28.86, 28.16, 27.56, 23.73, 14.42. MS (ESI-TOF) for C18H27N3 [M + H]+ calculated 286.2278, found 286.2240.

4-(5-Aminopentyl)-3-pentylquinolin-2-amine Dihydrochloride (14b)

Compound 14b was synthesized similarly as compound 9a. White solid (29 mg, 78%). 1H NMR (500 MHz, MeOD) δ 8.09 (d, J = 8.2 Hz, 1H), 7.76 (ddd, J = 1.2, 7.0, 8.3 Hz, 1H), 7.66 (d, J = 7.6 Hz, 1H), 7.56 (ddd, J = 1.2, 7.0, 8.3 Hz, 1H), 3.16 (t, J = 6.7 Hz, 2H), 2.97 (t, J = 7.5 Hz, 2H), 2.79 (t, J = 8.4 Hz, 2H), 1.80–1.64 (m, 6H), 1.64–1.56 (m, 2H), 1.54–1.46 (m, 2H), 1.48–1.38 (m, 2H), 0.96 (t, J = 7.3 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 154.78, 154.54, 135.97, 133.00, 126.70, 126.41, 124.30, 122.51, 118.60, 40.61, 32.81, 30.92, 29.79, 29.52, 28.48, 27.85, 27.54, 23.73, 14.41. MS (ESI-TOF) for C19H29N3 [M + H]+ calculated 300.2434, found 300.2397.

5-Bromo-3-pentylquinolin-2-amine (16)

To a solution of compound 15 (200 mg, 1 mmol) in DMSO (3 mL) were added heptanenitrile (275 μL, 2 mmol) and t-BuOK (224 mg, 2 mmol). The resulting reaction mixture was stirred for 3 h at 60 °C under nitrogen atmosphere. The reaction mixture was diluted with water and extracted with EtOAc (3 × 50 mL). The combined organic layer was dried over Na2SO4 and concentrated under reduced pressure. The crude material was purified by flash chromatography (50% EtOAc/hexanes) to obtain the compound 16 as an off-white solid (220 mg, 75%). 1H NMR (500 MHz, DMSO-d6) δ 7.82 (s, 1H), 7.49–7.40 (m, 2H), 7.34 (dd, J = 7.6, 8.3 Hz, 1H), 6.58 (s, 2H), 2.62 (t, J = 7.8 Hz, 2H), 1.66–1.57 (m, 2H), 1.44–1.29 (m, 4H), 0.89 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, DMSO-d6) δ 157.75, 147.59, 132.61, 128.85, 126.08, 124.89, 124.73, 121.98, 120.40, 30.96, 30.29, 27.42, 22.06, 14.01. MS (ESI-TOF) for C14H17BrN2 [M + H]+ calculated 293.0648, found 293.0684.

3-((2-Amino-3-pentylquinolin-5-yl)methyl)benzonitrile (17a)

To a solution of compound 16 (58.8 mg, 0.2 mmol) in THF (2 mL) were added 3-cyanobenzylzinc bromide (0.8 mL, 0.4 mmol, 0.5 M in THF) and Pd(PPh3)4 (11.6 mg, 0.01 mmol). The resulting reaction mixture was stirred at 65 °C under nitrogen atmosphere for 12 h. The reaction mixture was diluted with water and extracted with EtOAc (3 × 10 mL). The combined organic layer was dried over Na2SO4 and concentrated under reduced pressure. The crude material was purified by flash chromatography (60% EtOAc/hexanes) to obtain the compound 17a as a pale yellow solid (54 mg, 82%). 1H NMR (500 MHz, CDCl3) δ 7.67 (s, 1H), 7.61 (d, J = 8.5 Hz, 1H), 7.51–7.44 (m, 3H), 7.40–7.33 (m, 2H), 7.07 (d, J = 7.0 Hz, 1H), 4.80 (s, 2H), 4.37 (s, 2H), 2.52 (t, J = 7.6 Hz, 2H), 1.66–1.56 (m, 2H), 1.38–1.21 (m, 4H), 0.88 (t, J = 7.1 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 155.95, 147.28, 142.44, 134.55, 133.17, 132.16, 131.77, 130.13, 129.40, 128.69, 125.59, 124.49, 123.66, 122.91, 119.00, 112.68, 38.40, 31.52, 31.49, 27.56, 22.63, 14.15. MS (ESI-TOF) for C22H23N3 [M + H]+ calculated 330.1965, found 330.1896.

Compounds 17b–d

They were synthesized similarly as compound 17a.

4-((2-Amino-3-pentylquinolin-5-yl)methyl)benzonitrile (17b)

4-Cyanobenzylzinc bromide was used as reagent. Pale yellow solid (55 mg, 83%). 1H NMR (500 MHz, CDCl3) δ 7.66 (s, 1H), 7.62 (d, J = 8.5 Hz, 1H), 7.56 (d, J = 8.3 Hz, 2H), 7.48 (dd, J = 7.0, 8.4 Hz, 1H), 7.30–7.25 (m, 2H), 7.09 (d, J = 6.8 Hz, 1H), 4.81 (s, 2H), 4.41 (s, 2H), 2.52 (t, J = 7.8 Hz, 2H), 1.66–1.53 (m, 2H), 1.39–1.19 (m, 4H), 0.89 (t, J = 7.1 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 155.95, 147.26, 146.62, 134.50, 132.44, 131.82, 129.42, 128.68, 125.56, 124.54, 123.63, 122.96, 119.07, 110.20, 39.00, 31.51, 31.45, 27.53, 22.63, 14.15. MS (ESI-TOF) for C22H23N3 [M + H]+ calculated 330.1965, found 330.1899.

2-((2-Amino-3-pentylquinolin-5-yl)methyl)benzonitrile (17c)

2-Cyanobenzylzinc bromide was used as reagent. Pale yellow solid (45 mg, 68%). 1H NMR (500 MHz, CDCl3) δ 7.71 (s, 1H), 7.69 (dd, J = 1.1, 7.7 Hz, 1H), 7.61 (d, J = 8.5 Hz, 1H), 7.47 (dd, J = 7.1, 8.5 Hz, 1H), 7.39 (td, J = 1.4, 7.7 Hz, 1H), 7.29 (td, J = 1.2, 7.6 Hz, 1H), 7.07 (dd, J = 1.1, 7.1 Hz, 1H), 7.00 (dd, J = 0.6, 7.9 Hz, 1H), 4.81 (s, 2H), 4.57 (s, 2H), 2.53 (t, J = 7.6 Hz, 2H), 1.67–1.60 (m, 2H), 1.38–1.22 (m, 4H), 0.87 (t, J = 7.1 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 156.01, 147.18, 144.65, 134.08, 133.05, 132.87, 131.83, 129.79, 128.64, 126.92, 125.57, 124.59, 123.80, 123.06, 118.25, 112.43, 36.89, 31.56, 31.48, 27.55, 22.62, 14.16. MS (ESI-TOF) for C22H23N3 [M + H]+ calculated 330.1965, found 330.2008.

5-Benzyl-3-pentylquinolin-2-amine (17d)

Benzylzinc bromide was used as reagent. White solid (50 mg, 82%). 1H NMR (500 MHz, DMSO-d6) δ 7.82 (s, 1H), 7.41–7.31 (m, 2H), 7.28–7.18 (m, 4H), 7.18–7.11 (m, 1H), 7.05–7.00 (m, 1H), 6.21 (s, 2H), 4.28 (s, 2H), 2.55–2.49 (m, 2H), 1.57–1.47 (m, 2H), 1.32–1.17 (m, 4H), 0.83 (t, J = 7.2 Hz, 3H). 13C NMR (126 MHz, DMSO-d6) δ 156.73, 147.10, 141.09, 136.57, 131.20, 128.43, 128.28, 127.75, 125.84, 123.78, 123.50, 122.48, 121.73, 37.77, 30.72, 30.31, 27.23, 22.06, 13.96. MS (ESI-TOF) for C21H24N2 [M + H]+ calculated 305.2012, found 305.1951.

5-(3-(Aminomethyl)benzyl)-3-pentylquinolin-2-amine (18a)

A solution of compound 17a (33 mg, 0.1 mmol) in THF (5 mL) was added slowly to a solution of LiAlH4 (0.5 mL, 0.5 mmol, 1.0 M in THF) in THF (3 mL) at 0 °C under nitrogen atmosphere. The reaction mixture was stirred for 2 h at 25 °C and 2 h at 75 °C. The reaction mixture was carefully quenched with ice-cold water (1 mL) at 0 °C, and 10% NaOH (1 mL) was added. The resulting mixture was stirred for 10 min at room temperature, filtered through Celite, and washed with CH2Cl2 (15 mL). The resulting filtrate was dried over Na2SO4 and concentrated under reduced pressure and the crude material was purified by neutral-alumina column chromatography (20% MeOH/CH2Cl2) to obtain the compound 18a as a white solid (24 mg, 72%). 1H NMR (500 MHz, MeOD) δ 7.88 (s, 1H), 7.46–7.38 (m, 2H), 7.21 (t, J = 7.5 Hz, 1H), 7.18–7.10 (m, 3H), 7.06 (d, J = 7.4 Hz, 1H), 4.34 (s, 2H), 3.70 (s, 2H), 2.55 (t, J = 7.5 Hz, 2H), 1.60 (p, J = 7.6 Hz, 2H), 1.42–1.20 (m, 4H), 0.89 (t, J = 7.1 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 158.00, 147.60, 143.84, 142.65, 138.04, 133.82, 129.68, 129.58, 128.69, 128.24, 126.21, 125.12, 125.06, 124.29, 123.67, 46.67, 39.64, 32.47, 31.77, 28.68, 23.64, 14.41. MS (ESI-TOF) for C22H27N3 [M + H]+ calculated 334.2278, found 334.2214.

Compounds 18b and 18c

They were synthesized similarly as compound 18a.

5-(4-(Aminomethyl)benzyl)-3-pentylquinolin-2-amine (18b)

Compound 17b was used as reagent. White solid (25 mg, 75%). 1H NMR (500 MHz, MeOD) δ 7.87 (s, 1H), 7.51–7.37 (m, 2H), 7.22 (d, J = 8.0 Hz, 2H), 7.14 (d, J = 7.9 Hz, 2H), 7.12–7.09 (m, 1H), 4.32 (s, 2H), 3.72 (s, 2H), 2.54 (t, J = 7.6 Hz, 2H), 1.68–1.48 (m, 2H), 1.40–1.21 (m, 4H), 0.89 (t, J = 7.1 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 158.00, 147.60, 141.33, 141.04, 138.13, 133.81, 129.74, 129.56, 128.59, 125.10, 124.98, 124.27, 123.63, 46.35, 39.28, 32.48, 31.78, 28.66, 23.64, 14.41. MS (ESI-TOF) for C22H27N3 [M + H]+ calculated 334.2278, found 334.2191.

5-(2-(Aminomethyl)benzyl)-3-pentylquinolin-2-amine (18c)

Compound 17c was used as reagent. White solid (21 mg, 63%). 1H NMR (500 MHz, MeOD) δ 7.90 (s, 1H), 7.47–7.33 (m, 3H), 7.24 (td, J = 1.3, 7.5 Hz, 1H), 7.15 (td, J = 1.4, 7.5 Hz, 1H), 6.93 (dd, J = 1.3, 7.7 Hz, 1H), 6.84 (dd, J = 1.1, 7.1 Hz, 1H), 4.42 (s, 2H), 3.84 (s, 2H), 2.59 (t, J = 7.8 Hz, 2H), 1.68–1.57 (m, 2H), 1.40–1.27 (m, 4H), 0.90 (t, J = 7.1 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 158.12, 147.46, 141.29, 139.25, 137.80, 133.50, 131.09, 129.58, 129.13, 128.27, 127.89, 125.42, 124.27, 124.19, 123.78, 43.84, 35.93, 32.58, 31.94, 28.87, 23.65, 14.42. MS (ESI-TOF) for C22H27N3 [M + H]+ calculated 334.2278, found 334.2195.

3-((2-Amino-3-pentylquinolin-5-yl)methyl)benzamide (18d)

To a solution of compound 17a (33 mg, 0.1 mmol) in t-BuOH (2 mL) was added potassium hydroxide (84 mg, 1.5 mmol). The reaction mixture was stirred for 8 h at 60 °C. The reaction was allowed to cool to room temperature, the solvent was removed under reduced pressure and the crude solubilized in ethyl acetate. The organic layer was washed with water and saturated aqueous ammonium chloride and dried over Na2SO4 and evaporated under reduced pressure. The residue was purified by silica gel flash-column chromatography (15% MeOH/CH2Cl2) to afford the compound (18d) as a white solid (18 mg, 52%). 1H NMR (500 MHz, MeOD) δ 7.88 (s, 1H), 7.78 (d, J = 0.8 Hz, 1H), 7.68 (dt, J = 1.9, 7.0 Hz, 1H), 7.49–7.43 (m, 2H), 7.38–7.27 (m, 2H), 7.16 (dd, J = 3.2, 5.0 Hz, 1H), 4.42 (s, 2H), 2.56 (t, J = 7.1 Hz, 2H), 1.58 (p, J = 7.5 Hz, 2H), 1.36–1.27 (m, 2H), 1.28–1.19 (m, 2H), 0.86 (t, J = 7.2 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 172.26, 157.87, 147.04, 142.96, 137.61, 135.13, 134.03, 133.11, 129.84, 129.66, 128.98, 126.42, 125.39, 125.32, 124.08, 123.44, 39.47, 32.39, 31.68, 28.61, 23.59, 14.39. MS (ESI-TOF) for C22H25N3O [M + H]+ calculated 348.2070, found 348.2022.

3-(2-Amino-3-pentylquinolin-5-yl)benzonitrile (19a)

To a stirred solution of compound 16 (59 mg, 0.2 mmol) in 1,4-dioxane (2 mL) were added 3-cyanophenylboronic acid (44 mg, 0.3 mmol), Pd(dppf)Cl2 (14.6 mg, 0.02 mmol), and K2CO3 (83 mg, 0.6 mmol). The resulting reaction mixture was stirred for 12 h at 90 °C under nitrogen atmosphere. The reaction mixture was diluted with water and extracted with EtOAc (3 × 20 mL). The combined organic layer was dried over Na2SO4 and concentrated under reduced pressure, and crude material was purified by flash chromatography (60% EtOAc/hexanes) to obtain the compound 19a as a brownish solid (40 mg, 63%). 1H NMR (500 MHz, CDCl3) δ 7.77–7.66 (m, 4H), 7.64–7.52 (m, 3H), 7.15 (dd, J = 1.2, 7.1 Hz, 1H), 4.89 (s, 2H), 2.53 (t, J = 7.6 Hz, 2H), 1.67–1.57 (m, 2H), 1.39–1.31 (m, 4H), 0.89 (t, J = 6.9 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 156.25, 146.96, 141.74, 137.22, 134.46, 133.42, 132.79, 131.10, 129.35, 128.42, 126.31, 124.37, 123.92, 122.25, 118.90, 112.78, 31.69, 31.59, 27.74, 22.57, 14.15. MS (ESI-TOF) for C21H21N3 [M + H]+ calculated 316.1808, found 316.1823.

4-(2-Amino-3-pentylquinolin-5-yl)benzonitrile (19b)

Compound 19b was synthesized similarly as compound 19a. 4-Cyanophenylboronic acid was used as reagent. Brownish solid (38 mg, 60%). 1H NMR (500 MHz, CDCl3) δ 7.83–7.76 (m, 2H), 7.71 (d, J = 8.4 Hz, 1H), 7.61 (s, 1H), 7.60–7.53 (m, 3H), 7.17 (dd, J = 1.2, 7.2 Hz, 1H), 4.89 (s, 2H), 2.52 (t, J = 7.7 Hz, 2H), 1.67–1.55 (m, 2H), 1.40–1.31 (m, 4H), 0.89 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 156.24, 146.97, 145.32, 137.73, 132.84, 132.32, 130.78, 128.40, 126.40, 124.35, 123.80, 122.09, 119.04, 111.30, 31.68, 31.56, 27.73, 22.57, 14.16. MS (ESI-TOF) for C21H21N3 [M + H]+ calculated 316.1808, found 316.1845.

Compounds 20a,b

They were synthesized similarly as compound 18a.

5-(3-(Aminomethyl)phenyl)-3-pentylquinolin-2-amine (20a)

Compound 19a was used as reagent. White solid (21 mg, 66%). 1H NMR (500 MHz, MeOD) δ 7.73 (s, 1H), 7.58–7.39 (m, 5H), 7.30 (d, J = 6.7 Hz, 1H), 7.16 (d, J = 6.6 Hz, 1H), 3.88 (s, 2H), 2.56 (t, J = 7.6 Hz, 2H), 1.68–1.53 (m, 2H), 1.38–1.29 (m, 4H), 0.90 (t, J = 6.7 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 158.28, 147.40, 144.04, 141.73, 141.28, 134.86, 130.00, 129.55, 129.53, 129.41, 127.59, 125.60, 124.69, 124.34, 123.07, 46.69, 32.56, 31.81, 28.73, 23.59, 14.39. MS (ESI-TOF) for C21H25N3 [M + H]+ calculated 320.2121, found 320.2072.

5-(4-(Aminomethyl)phenyl)-3-pentylquinolin-2-amine (20b)

Compound 19b was used as reagent. White solid (20 mg, 63%). 1H NMR (500 MHz, MeOD) δ 7.72 (s, 1H), 7.57–7.45 (m, 4H), 7.39 (d, J = 8.1 Hz, 2H), 7.13 (dd, J = 1.7, 6.6 Hz, 1H), 3.89 (s, 2H), 2.54 (t, J = 7.6 Hz, 2H), 1.67–1.51 (m, 2H), 1.38–1.26 (m, 4H), 0.89 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 158.26, 147.42, 142.97, 141.07, 140.07, 134.82, 131.06, 129.43, 128.56, 125.58, 124.65, 124.33, 123.07, 46.45, 32.58, 31.88, 28.78, 23.57, 14.40. MS (ESI-TOF) for C21H25N3 [M + H]+ calculated 320.2121, found 320.2073.

5-(3-Aminopropyl)-3-pentylquinolin-2-amine (23)

A solution of 16 (147 mg, 0.5 mmol) and acrylonitrile (66 μL, 1 mmol) in DMF (4 mL) was treated with Pd(OAc)2 (11.2 mg, 0.05 mmol), PPh3 (26.2 mg, 0.1 mmol), and K2CO3 (138 mg, 1 mmol). The resulting reaction mixture was stirred for 12 h at 110 °C under nitrogen atmosphere. The reaction mixture was diluted with water and extracted with EtOAc (3 × 20 mL). The combined organic layer was dried over Na2SO4 and concentrated under reduced pressure. The crude material was purified by flash chromatography (60% EtOAc/hexanes) to obtain the compound 21 as a pale yellow solid (73 mg, 55%). MS (ESI-TOF) for C17H19N3 [M + H]+ calculated 266.1652, found 266.1663. To a solution of compound 21 (53 mg, 0.2 mmol) in anhydrous EtOAc (10 mL) was added a catalytic amount of Pt/C, and the reaction mixture was subjected to hydrogenation at 30 psi for 3 h. The reaction mixture was filtered, and the filtrate concentrated under reduced pressure. The crude material was purified using silica gel column chromatography (60% EtOAc/hexanes) to obtain compound 22 as white solid (40 mg, 75%). MS (ESI-TOF) for C17H21N3 [M + H]+ calculated 268.1808, found 268.1821. A solution of compound 22 (27 mg, 0.1 mmol) in THF (5 mL) was added slowly to a solution of LiAlH4 (0.5 mL, 0.5 mmol, 1.0 M in THF) in THF (3 mL) at 0 °C under nitrogen atmosphere. The reaction mixture was stirred for 2 h at 25 °C and 2 h at 60 °C. The reaction mixture was carefully quenched with ice-cold water (1 mL) at 0 °C, and 10% NaOH (1 mL) was added. The resulting mixture was stirred for 10 min at room temperature, filtered through Celite, and washed with CH2Cl2 (15 mL). The resulting filtrate was dried over Na2SO4 and concentrated under reduced pressure and the crude material was purified by flash neutral-alumina column chromatography (20% MeOH/CH2Cl2) to obtain the compound 23 as a white solid (15 mg, 55%). 1H NMR (500 MHz, MeOD) δ 7.99 (s, 1H), 7.40–7.37 (m, 2H), 7.09 (dd, J = 2.8, 5.4 Hz, 1H), 3.02 (t, J = 7.5 Hz, 2H), 2.73 (t, J = 7.2 Hz, 2H), 2.68 (t, J = 7.6 Hz, 2H), 1.92–1.80 (m, 2H), 1.78–1.68 (m, 2H), 1.48–1.40 (m, 4H), 0.95 (t, J = 7.1 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 158.00, 147.49, 139.44, 133.35, 129.58, 125.36, 123.72, 123.66, 123.41, 42.35, 35.26, 32.80, 32.15, 30.76, 29.17, 23.69, 14.46. MS (ESI-TOF) for C17H25N3 [M + H]+ calculated 272.2121, found 272.2155.

Compounds 27–29

They were synthesized similarly as compound 16.

6-Bromo-3-pentylquinolin-2-amine (27)

Compound 24 was used as reagent. White solid (230 mg, 78%). 1H NMR (500 MHz, CDCl3) δ 7.74 (d, J = 2.2 Hz, 1H), 7.58 (s, 1H), 7.56 (dd, J = 2.2, 8.9 Hz, 1H), 7.51 (d, J = 8.8 Hz, 1H), 4.87 (s, 2H), 2.57 (t, J = 7.7 Hz, 2H), 1.78–1.66 (m, 2H), 1.45–1.36 (m, 4H), 0.93 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 156.49, 145.21, 134.44, 132.05, 129.08, 127.43, 125.84, 124.79, 115.57, 31.76, 31.24, 27.56, 22.67, 14.17. MS (ESI-TOF) for C14H17BrN2 [M + H]+ calculated 293.0648, found 293.0654.

7-Bromo-3-pentylquinolin-2-amine (28)

Compound 25 was used as reagent. Yellow solid (220 mg, 75%). 1H NMR (500 MHz, CDCl3) δ 7.81 (d, J = 2.2 Hz, 1H), 7.63 (s, 1H), 7.45 (d, J = 8.5 Hz, 1H), 7.32 (dd, J = 1.9, 8.5 Hz, 1H), 4.93 (s, 2H), 2.55 (t, J = 7.9 Hz, 2H), 1.76–1.67 (m, 2H), 1.44–1.36 (m, 4H), 0.93 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 156.88, 147.41, 135.17, 128.30, 128.09, 125.98, 124.16, 123.19, 122.73, 31.79, 31.24, 27.56, 22.67, 14.17. MS (ESI-TOF) for C14H17BrN2 [M + H]+ calculated 293.0648, found 293.0669.

8-Bromo-3-pentylquinolin-2-amine (29)

Compound 26 was used as reagent. Pale yellow solid (250 mg, 85%). 1H NMR (500 MHz, CDCl3) δ 7.82 (dd, J = 1.4, 7.5 Hz, 1H), 7.65 (s, 1H), 7.55 (dd, J = 1.4, 7.9 Hz, 1H), 7.08 (t, J = 7.7 Hz, 1H), 5.04 (s, 2H), 2.58 (t, J = 7.5 Hz, 2H), 1.78–1.65 (m, 2H), 1.48–1.30 (m, 4H), 0.92 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 157.09, 143.79, 135.84, 132.41, 126.93, 125.67, 124.65, 122.94, 120.61, 31.76, 31.08, 27.58, 22.67, 14.16. MS (ESI-TOF) for C14H17BrN2 [M + H]+ calculated 293.0648, found 293.0675.

Compounds 30a–c, 31a–c, 32a–c, and 33

They were synthesized similarly as compound 17a.

4-(2-Amino-3-pentylquinolin-5-yl)butanenitrile (30a)

Compound 16 and 3-cyanopropylzinc bromide were used as reagents. White solid (44 mg, 78%). 1H NMR (500 MHz, CDCl3) δ 7.86 (s, 1H), 7.56 (d, J = 8.4 Hz, 1H), 7.44 (dd, J = 7.1, 8.4 Hz, 1H), 7.10 (dd, J = 1.1, 7.1 Hz, 1H), 4.83 (s, 2H), 3.15 (t, J = 7.4 Hz, 2H), 2.62 (t, J = 7.7 Hz, 2H), 2.36 (t, J = 7.0 Hz, 2H), 2.12–2.01 (m, 2H), 1.79–1.68 (m, 2H), 1.45–1.37 (m, 4H), 0.93 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 155.95, 147.16, 135.47, 131.33, 128.61, 125.08, 123.79, 123.28, 122.75, 119.71, 31.84, 31.77, 31.02, 27.95, 26.64, 22.66, 16.84, 14.21. MS (ESI-TOF) for C18H23N3 [M + H]+ calculated 282.1965, found 282.1904.

5-(2-Amino-3-pentylquinolin-5-yl)pentanenitrile (30b)

Compound 16 and 4-cyanobutylzinc bromide were used as reagents. Off-white solid (45 mg, 76%). 1H NMR (500 MHz, CDCl3) δ 7.84 (s, 1H), 7.54 (d, J = 8.4 Hz, 1H), 7.43 (dd, J = 7.1, 8.4 Hz, 1H), 7.07 (dd, J = 1.1, 7.1 Hz, 1H), 4.80 (s, 2H), 3.02 (t, J = 7.5 Hz, 2H), 2.62 (t, J = 7.6 Hz, 2H), 2.37 (t, J = 7.1 Hz, 2H), 1.93–1.83 (m, 2H), 1.80–1.69 (m, 4H), 1.47–1.36 (m, 4H), 0.93 (t, J = 7.1 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 155.86, 147.12, 136.99, 131.59, 128.56, 124.66, 123.49, 123.01, 122.83, 119.68, 31.82, 31.77, 31.69, 29.93, 27.97, 25.25, 22.67, 17.27, 14.22. MS (ESI-TOF) for C19H25N3 [M + H]+ calculated 296.2121, found 296.2068.

6-(2-Amino-3-pentylquinolin-5-yl)hexanenitrile (30c)

Compound 16 and 5-cyanopentylzinc bromide were used as reagents. White solid (38 mg, 61%). 1H NMR (500 MHz, CDCl3) δ 7.84 (s, 1H), 7.53 (d, J = 8.4 Hz, 1H), 7.42 (dd, J = 7.1, 8.4 Hz, 1H), 7.07 (dd, J = 1.2, 7.0 Hz, 1H), 4.80 (s, 2H), 2.99 (t, J = 7.6 Hz, 2H), 2.62 (t, J = 7.7 Hz, 2H), 2.34 (t, J = 7.1 Hz, 2H), 1.80–1.64 (m, 6H), 1.62–1.53 (m, 2H), 1.45–1.36 (m, 4H), 0.93 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 155.81, 147.02, 137.81, 131.78, 128.58, 124.38, 123.33, 122.91, 122.86, 119.84, 32.30, 31.79, 31.75, 30.36, 28.78, 27.98, 25.48, 22.68, 17.29, 14.22. MS (ESI-TOF) for C20H27N3 [M + H]+ calculated 310.2278, found 310.2323.

4-(2-Amino-3-pentylquinolin-6-yl)butanenitrile (31a)

Compound 27 and 3-cyanopropylzinc bromide were used as reagents. White solid (35 mg, 62%). 1H NMR (500 MHz, CDCl3) δ 7.64 (s, 1H), 7.60 (d, J = 8.5 Hz, 1H), 7.41 (d, J = 2.0 Hz, 1H), 7.34 (dd, J = 2.1, 8.5 Hz, 1H), 4.80 (s, 2H), 2.89 (t, J = 7.3 Hz, 2H), 2.58 (t, J = 7.7 Hz, 2H), 2.33 (t, J = 7.1 Hz, 2H), 2.13–1.95 (m, 2H), 1.79–1.65 (m, 2H), 1.45–1.36 (m, 4H), 0.93 (t, J = 7.1 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 156.14, 145.35, 135.19, 133.81, 129.65, 126.26, 126.06, 124.58, 124.15, 119.73, 34.18, 31.80, 31.31, 27.71, 27.02, 22.69, 16.47, 14.19. MS (ESI-TOF) for C18H23N3 [M + H]+ calculated 282.1965, found 282.1832.

5-(2-Amino-3-pentylquinolin-6-yl)pentanenitrile (31b)

Compound 27 and 4-cyanobutylzinc bromide were used as reagents. Pale yellow solid (39 mg, 66%). 1H NMR (500 MHz, CDCl3) δ 7.63 (s, 1H), 7.59 (d, J = 8.5 Hz, 1H), 7.37 (d, J = 1.9 Hz, 1H), 7.34 (dd, J = 2.1, 8.5 Hz, 1H), 4.78 (s, 2H), 2.76 (t, J = 7.4 Hz, 2H), 2.57 (t, J = 7.8 Hz, 2H), 2.36 (t, J = 7.1 Hz, 2H), 1.89–1.80 (m, 2H), 1.76–1.69 (m, 4H), 1.48–1.30 (m, 4H), 0.93 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 155.97, 145.13, 135.46, 135.22, 129.91, 125.82, 125.76, 124.56, 123.98, 119.80, 34.84, 31.80, 31.32, 30.41, 27.74, 24.96, 22.70, 17.26, 14.19. MS (ESI-TOF) for C19H25N3 [M + H]+ calculated 296.2121, found 296.2146.

6-(2-Amino-3-pentylquinolin-6-yl)hexanenitrile (31c)

Compound 27 and 5-cyanopentylzinc bromide were used as reagents. Pale yellow solid (40 mg, 65%). 1H NMR (500 MHz, CDCl3) δ 7.63 (s, 1H), 7.58 (d, J = 8.5 Hz, 1H), 7.37 (d, J = 1.9 Hz, 1H), 7.34 (dd, J = 2.1, 8.5 Hz, 1H), 4.77 (s, 2H), 2.73 (t, J = 7.6 Hz, 2H), 2.57 (t, J = 7.7 Hz, 2H), 2.33 (t, J = 7.1 Hz, 2H), 1.78–1.61 (m, 6H), 1.56–1.46 (m, 2H), 1.44–1.36 (m, 4H), 0.93 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 155.89, 145.03, 136.28, 135.24, 130.01, 125.75, 125.63, 124.55, 123.88, 119.93, 35.44, 31.81, 31.33, 30.77, 28.42, 27.76, 25.47, 22.70, 17.27, 14.19. MS (ESI-TOF) for C20H27N3 [M + H]+ calculated 310.2278, found 310.2309.

4-(2-Amino-3-pentylquinolin-7-yl)butanenitrile (32a)

Compound 28 and 3-cyanopropylzinc bromide were used as reagents. Pale yellow solid (33 mg, 59%). 1H NMR (500 MHz, CDCl3) δ 7.66 (s, 1H), 7.55 (d, J = 8.1 Hz, 1H), 7.45 (s, 1H), 7.09 (dd, J = 1.7, 8.1 Hz, 1H), 4.83 (s, 2H), 2.91 (t, J = 7.3 Hz, 2H), 2.57 (t, J = 7.6 Hz, 2H), 2.34 (t, J = 7.1 Hz, 2H), 2.12–2.02 (m, 2H), 1.78–1.68 (m, 2H), 1.51–1.31 (m, 4H), 0.93 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 156.54, 146.63, 140.61, 135.31, 127.40, 124.69, 123.73, 123.46, 123.24, 119.70, 34.72, 31.80, 31.27, 27.73, 26.85, 22.69, 16.52, 14.19. MS (ESI-TOF) for C18H23N3 [M + H]+ calculated 282.1965, found 282.1978.

5-(2-Amino-3-pentylquinolin-7-yl)pentanenitrile (32b)

Compound 28 and 4-cyanobutylzinc bromide were used as reagents. Off-white solid (36 mg, 61%). 1H NMR (500 MHz, CDCl3) δ 7.66 (s, 1H), 7.54 (d, J = 8.1 Hz, 1H), 7.43 (s, 1H), 7.09 (dd, J = 1.7, 8.2 Hz, 1H), 4.81 (s, 2H), 2.79 (t, J = 7.4 Hz, 2H), 2.57 (t, J = 7.6 Hz, 2H), 2.34 (t, J = 7.1 Hz, 2H), 1.94–1.81 (m, 2H), 1.77–1.63 (m, 4H), 1.45–1.36 (m, 4H), 0.93 (t, 3H). 13C NMR (126 MHz, CDCl3) δ 156.44, 146.56, 142.18, 135.36, 127.15, 124.52, 123.82, 123.20, 123.00, 119.77, 35.26, 31.80, 31.26, 30.06, 27.75, 24.87, 22.69, 17.22, 14.19. MS (ESI-TOF) for C19H25N3 [M + H]+ calculated 296.2121, found 296.2168.

6-(2-Amino-3-pentylquinolin-7-yl)hexanenitrile (32c)

Compound 28 and 5-cyanopentylzinc bromide were used as reagents. Pale yellow solid (39 mg, 63%). MS (ESI-TOF) for C20H27N3 [M + H]+ calculated 310.2278, found 310.2309.

4-(2-Amino-3-pentylquinolin-8-yl)butanenitrile (33)

Compound 29 and 3-cyanopropylzinc bromide were used as reagents. Pale yellow solid (30 mg, 53%). 1H NMR (500 MHz, CDCl3) δ 7.66 (s, 1H), 7.49 (dd, J = 1.5, 8.0 Hz, 1H), 7.35 (dd, J = 1.4, 7.1 Hz, 1H), 7.16 (dd, J = 7.1, 8.0 Hz, 1H), 4.79 (s, 2H), 3.23 (t, J = 7.2 Hz, 2H), 2.58 (t, J = 7.6 Hz, 2H), 2.32 (t, J = 7.1 Hz, 2H), 2.19–2.09 (m, 2H), 1.79–1.66 (m, 2H), 1.45–1.33 (m, 4H), 0.93 (t, J = 7.1 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 155.58, 145.03, 135.76, 135.33, 128.76, 125.91, 124.72, 123.64, 122.30, 120.54, 31.83, 31.28, 30.49, 27.78, 26.53, 22.70, 16.95, 14.19. MS (ESI-TOF) for C18H23N3 [M + H]+ calculated 282.1965, found 282.2008.

Compounds 34a–c

They were synthesized similarly as compound 18a.

5-(4-Aminobutyl)-3-pentylquinolin-2-amine (34a)

Compound 30a was used as reagent. White solid (20 mg, 70%). 1H NMR (500 MHz, MeOD) δ 7.95 (s, 1H), 7.42–7.35 (m, 2H), 7.08 (dd, J = 3.1, 5.1 Hz, 1H), 3.00 (t, J = 7.6 Hz, 2H), 2.69–2.63 (m, 4H), 1.78–1.64 (m, 4H), 1.61–1.50 (m, 2H), 1.46–1.40 (m, 4H), 0.95 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 157.97, 147.47, 139.74, 133.37, 129.56, 125.18, 123.77, 123.64, 123.41, 42.51, 33.75, 33.21, 32.72, 32.07, 29.82, 29.05, 23.68, 14.47. MS (ESI-TOF) for C18H27N3 [M + H]+ calculated 286.2278, found 286.2218.

5-(5-Aminopentyl)-3-pentylquinolin-2-amine (34b)

Compound 30b was used as reagent. White solid (21 mg, 70%). 1H NMR (500 MHz, MeOD) δ 7.94 (s, 1H), 7.42–7.32 (m, 2H), 7.06 (dd, J = 2.9, 5.4 Hz, 1H), 2.98 (t, J = 7.6 Hz, 2H), 2.67 (t, J = 7.6 Hz, 2H), 2.62 (t, J = 7.0 Hz, 2H), 1.78–1.65 (m, 4H), 1.57–1.47 (m, 2H), 1.49–1.39 (m, 6H), 0.95 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 157.96, 147.46, 139.91, 133.37, 129.57, 125.12, 123.73, 123.58, 123.39, 42.53, 33.77, 33.35, 32.69, 32.39, 32.04, 29.03, 27.94, 23.68, 14.47. MS (ESI-TOF) for C19H29N3 [M + H]+ calculated 300.2434, found 300.2374.

5-(6-Aminohexyl)-3-pentylquinolin-2-amine (34c)

Compound 30c was used as reagent. White solid (18 mg, 57%). 1H NMR (500 MHz, MeOD) δ 7.95 (s, 1H), 7.41–7.32 (m, 2H), 7.06 (dd, J = 3.0, 5.3 Hz, 1H), 2.98 (t, J = 7.6 Hz, 2H), 2.67 (t, J = 7.4 Hz, 2H), 2.63 (t, J = 7.0 Hz, 2H), 1.71 (dq, J = 7.8, 15.5 Hz, 4H), 1.50–1.37 (m, 10H), 0.95 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 157.96, 147.45, 140.00, 133.37, 129.56, 125.08, 123.72, 123.55, 123.39, 42.40, 33.46, 33.34, 32.68, 32.51, 32.00, 30.48, 28.99, 27.93, 23.68, 14.47. MS (ESI-TOF) for C20H31N3 [M + H]+ calculated 314.2591, found 314.2537.

4-(2-Amino-3-pentylquinolin-5-yl)butanamide (34d)

Compound 34d was synthesized similarly as compound 18d. Compound 30a was used as reagent. White solid (15 mg, 50%). 1H NMR (500 MHz, MeOD) δ 8.02 (s, 1H), 7.45–7.31 (m, 2H), 7.08 (dd, J = 2.9, 5.4 Hz, 1H), 3.01 (t, J = 7.7 Hz, 2H), 2.68 (t, J = 7.7 Hz, 2H), 2.30 (t, J = 7.3 Hz, 2H), 2.03–1.91 (m, 2H), 1.80–1.66 (m, 2H), 1.48–1.38 (m, 4H), 0.94 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 178.76, 157.96, 147.27, 139.18, 133.57, 129.64, 125.45, 123.92, 123.69, 123.43, 35.95, 32.85, 32.76, 32.13, 29.12, 28.38, 23.68, 14.47. MS (ESI-TOF) for C18H25N3O [M + H]+ calculated 300.2070, found 300.2025.

1-(4-(2-Amino-3-pentylquinolin-5-yl)butyl)guanidine (34e)

1H-Pyrazole-1-carboxamidine hydrochloride (16 mg, 0.11 mmol) and Et3N (15.3 μL, 0.11 mmol) were added to a solution of compound 34a (28.5 mg, 0.1 mmol) in MeOH (2 mL), and the reaction mixture was stirred for 3 h at room temperature. The solvent was removed under reduced pressure and the crude material was purified by basic-alumina column chromatography (30% MeOH/CH2Cl2) to obtain 34e as a white solid (16 mg, 49%). 1H NMR (500 MHz, DMSO-d6) δ 7.82 (s, 1H), 7.60 (t, J = 5.7 Hz, 1H), 7.36–7.24 (m, 3H), 6.98 (dd, J = 3.1, 5.3 Hz, 1H), 6.84 (s, 2H), 6.22 (s, 2H), 3.13 (q, J = 6.9 Hz, 2H), 2.92 (t, J = 7.5 Hz, 2H), 2.60 (t, J = 7.6 Hz, 2H), 1.68–1.56 (m, 4H), 1.58–1.46 (m, 2H), 1.39–1.29 (m, 4H), 0.88 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, DMSO-d6) δ 156.72, 156.66, 146.95, 137.62, 130.71, 127.62, 123.66, 123.27, 121.56, 121.26, 40.52, 31.08, 30.96, 30.56, 28.36, 27.64, 27.62, 22.03, 14.00. MS (ESI-TOF) for C19H29N5 [M + H]+ calculated 328.2496, found 328.2444.

Compounds 35a–c, 36a–c, and 37

They were synthesized similarly as compound 18a.

6-(4-Aminobutyl)-3-pentylquinolin-2-amine (35a)

Compound 31a was used as reagent. White solid (16 mg, 56%). 1H NMR (500 MHz, MeOD) δ 7.70 (s, 1H), 7.48–7.40 (m, 2H), 7.36 (dd, J = 2.0, 8.5 Hz, 1H), 2.73 (t, J = 7.5 Hz, 2H), 2.66 (t, J = 7.3 Hz, 2H), 2.62 (t, J = 7.5 Hz, 2H), 1.76–1.66 (m, 4H), 1.57–1.47 (m, 2H), 1.46–1.39 (m, 4H), 0.94 (t, J = 7.1 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 158.06, 145.47, 137.66, 136.72, 131.08, 126.94, 125.75, 125.30, 124.97, 42.38, 36.34, 33.20, 32.78, 31.81, 29.96, 28.96, 23.68, 14.43. MS (ESI-TOF) for C18H27N3 [M + H]+ calculated 286.2278, found 286.2283.

6-(5-Aminopentyl)-3-pentylquinolin-2-amine (35b)

Compound 31b was used as reagent. Off-white solid (19 mg, 63%). 1H NMR (500 MHz, MeOD) δ 7.70 (s, 1H), 7.45 (d, J = 8.5 Hz, 1H), 7.41 (s, 1H), 7.35 (dd, J = 2.0, 8.5 Hz, 1H), 2.72 (t, J = 7.6 Hz, 2H), 2.66–2.58 (m, 4H), 1.76–1.65 (m, 4H), 1.55–1.48 (m, 2H), 1.47–1.35 (m, 6H), 0.95 (t, J = 6.9 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 158.03, 145.42, 137.86, 136.72, 131.09, 126.88, 125.73, 125.30, 124.92, 42.50, 36.48, 33.66, 32.80, 32.61, 31.82, 28.97, 27.61, 23.68, 14.43. MS (ESI-TOF) for C19H29N3 [M + H]+ calculated 300.2434, found 300.2487.

6-(6-Aminohexyl)-3-pentylquinolin-2-amine (35c)

Compound 31c was used as reagent. Off-white solid (20 mg, 64%). 1H NMR (500 MHz, MeOD) δ 7.70 (s, 1H), 7.44 (d, J = 8.5 Hz, 1H), 7.40 (s, 1H), 7.34 (dd, J = 2.0, 8.5 Hz, 1H), 2.70 (t, J = 7.6 Hz, 2H), 2.65–2.57 (m, 4H), 1.76–1.62 (m, 4H), 1.49–1.33 (m, 10H), 0.94 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 158.02, 145.41, 137.96, 136.71, 131.10, 126.86, 125.72, 125.30, 124.90, 42.52, 36.50, 33.73, 32.80, 32.70, 31.83, 30.18, 28.97, 27.89, 23.68, 14.44. MS (ESI-TOF) for C20H31N3 [M + H]+ calculated 314.2591, found 314.2649.

7-(4-Aminobutyl)-3-pentylquinolin-2-amine (36a)

Compound 32a was used as reagent. Off-white solid (19 mg, 67%). 1H NMR (500 MHz, MeOD) δ 7.71 (s, 1H), 7.53 (d, J = 8.1 Hz, 1H), 7.33 (s, 1H), 7.10 (dd, J = 1.7, 8.2 Hz, 1H), 2.75 (t, J = 7.6 Hz, 2H), 2.65 (t, J = 7.2 Hz, 2H), 2.61 (t, J = 7.6 Hz, 2H), 1.78–1.65 (m, 4H), 1.58–1.48 (m, 2H), 1.46–1.39 (m, 4H), 0.94 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 158.52, 147.11, 144.79, 136.77, 128.05, 124.90, 124.62, 123.96, 123.62, 42.44, 36.97, 33.45, 32.77, 31.75, 29.78, 28.97, 23.68, 14.42. MS (ESI-TOF) for C18H27N3 [M + H]+ calculated 286.2278, found 286.2287.

7-(5-Aminopentyl)-3-pentylquinolin-2-amine (36b)

Compound 32b was used as reagent. White solid (18 mg, 60%). 1H NMR (500 MHz, MeOD) δ 7.71 (s, 1H), 7.53 (d, J = 8.1 Hz, 1H), 7.32 (s, 1H), 7.08 (dd, J = 1.7, 8.1 Hz, 1H), 2.74 (t, J = 7.6 Hz, 2H), 2.65–2.58 (m, 4H), 1.76–1.66 (m, 4H), 1.56–1.47 (m, 2H), 1.46–1.36 (m, 6H), 0.94 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 158.52, 147.10, 144.96, 136.78, 128.02, 124.88, 124.64, 123.90, 123.58, 42.47, 37.08, 33.62, 32.78, 32.38, 31.75, 28.97, 27.62, 23.68, 14.43. MS (ESI-TOF) for C19H29N3 [M + H]+ calculated 300.2434, found 300.2486.

7-(6-Aminohexyl)-3-pentylquinolin-2-amine (36c)

Compound 32c was used as reagent. White solid (20 mg, 64%). 1H NMR (500 MHz, MeOD) δ 7.71 (d, J = 0.9 Hz, 1H), 7.53 (d, J = 8.2 Hz, 1H), 7.32 (s, 1H), 7.08 (dd, J = 1.7, 8.1 Hz, 1H), 2.73 (t, J = 7.6 Hz, 2H), 2.66–2.56 (m, 4H), 1.78–1.65 (m, 4H), 1.55–1.35 (m, 10H), 0.94 (t, J = 7.1 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 158.50, 147.09, 145.03, 136.78, 128.00, 124.86, 124.65, 123.89, 123.56, 42.40, 37.07, 33.42, 32.79, 32.43, 31.75, 30.14, 28.98, 27.85, 23.69, 14.43. MS (ESI-TOF) for C20H31N3 [M + H]+ calculated 314.2591, found 314.2646.

8-(4-Aminobutyl)-3-pentylquinolin-2-amine (37)

Compound 33 was used as reagent. White solid (17 mg, 60%). 1H NMR (500 MHz, MeOD) δ 7.68 (s, 1H), 7.44 (dd, J = 1.5, 8.0 Hz, 1H), 7.32 (dd, J = 1.4, 7.1 Hz, 1H), 7.10 (dd, J = 7.1, 8.0 Hz, 1H), 3.06 (t, J = 7.7 Hz, 2H), 2.69 (t, J = 7.1 Hz, 2H), 2.62 (t, J = 7.7 Hz, 2H), 1.81–1.68 (m, 4H), 1.61–1.51 (m, 2H), 1.46–1.39 (m, 4H), 0.94 (t, J = 6.9 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 157.96, 145.92, 137.83, 137.02, 129.40, 126.33, 125.61, 125.14, 122.79, 42.40, 33.63, 32.83, 32.10, 31.86, 28.96, 28.93, 23.69, 14.43. MS (ESI-TOF) for C18H27N3 [M + H]+ calculated 286.2278, found 286.2283.

2-Amino-4,6-dibromobenzaldehyde (40)

A solution of compound 38 (737 mg, 2.5 mmol) in THF (20 mL) was added slowly to a solution of LiAlH4 (10 mL, 10 mmol, 1.0 M in THF) in THF (10 mL) at 0 °C under nitrogen atmosphere. The reaction mixture was stirred for 4 h at 25 °C. The reaction mixture was carefully quenched with ice-cold water (1 mL) at 0 °C, and 10% NaOH (1 mL) was added. The resulting mixture was stirred for 10 min at room temperature, filtered through Celite and washed with CH2Cl2 (50 mL). The resulting filtrate was dried over Na2SO4 and concentrated under reduced pressure and the crude material was purified by flash column chromatography (30% EtOAc/hexanes) to obtain the compound 39 as a off-white solid (386 mg, 55%). MS (ESI-TOF) for C7H7Br2NO [M + H]+ calculated 279.8967, found 279.8975. To a solution of compound 39 (351 mg, 1.25 mmol) in CH2Cl2 (10 mL) was added MnO2 (326 mg, 3.75 mmol, activated). The mixture was stirred for 6 h and then filtered over Celite. The mixture was concentrated and purified by flash chromatography (20% EtOAc/hexanes) to give compound 40 as a yellow solid (286 mg, 82%). 1H NMR (400 MHz, CDCl3) δ 10.33 (s, 1H), 7.07 (d, J = 1.8 Hz, 1H), 6.81 (d, J = 1.1 Hz, 1H), 6.56 (s, 2H). 13C NMR (126 MHz, CDCl3) δ 194.69, 152.20, 130.08, 129.98, 124.03, 118.97, 113.96. MS (ESI-TOF) for C7H5Br2NO [M + H]+ calculated 277.8811, found 277.8811.

5,7-Dibromo-3-pentylquinolin-2-amine (41)

Compound 41 was synthesized similarly as compound 16. Compound 40 was used as reagent. Off-white solid (242 mg, 65%). 1H NMR (400 MHz, CDCl3) δ 7.96 (s, 1H), 7.77 (dd, J = 0.8, 1.9 Hz, 1H), 7.61 (d, J = 1.9 Hz, 1H), 4.98 (s, 2H), 2.58 (t, J = 7.6 Hz, 2H), 1.81–1.68 (m, 2H), 1.48–1.36 (m, 4H), 0.94 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, CDCl3) δ 157.24, 147.77, 134.54, 128.98, 128.00, 125.45, 122.50, 121.99, 121.86, 31.78, 31.35, 27.55, 22.65, 14.18. MS (ESI-TOF) for C14H16Br2N2 [M + H]+ calculated 370.9753, found 370.9747.

5,5′-(2-Amino-3-pentylquinoline-5,7-diyl)bis(pentan-1-amine) (43)

To a solution of compound 41 (74 mg, 0.2 mmol) in THF (2 mL) were added 4-cyanobutylzinc bromide (1.6 mL, 0.8 mmol, 0.5 M in THF) and Pd(PPh3)4 (23 mg, 0.02 mmol). The resulting reaction mixture was stirred at 65 °C under nitrogen atmosphere for 24 h. The reaction mixture was diluted with water and extracted with EtOAc (3 × 10 mL). The combined organic layer was dried over Na2SO4 and concentrated under reduced pressure. The crude material was purified by flash chromatography (20% MeOH/CH2Cl2) to obtain the compound 42 as a pale yellow solid (19 mg, 25%). MS (ESI-TOF) for C24H32N4 [M + H]+ calculated 377.2700, found 377.2691. A solution of compound 42 (19 mg, 0.05 mmol) in THF (5 mL) was added slowly to a solution of LiAlH4 (0.5 mL, 0.5 mmol, 1.0 M in THF) in THF (3 mL) at 0 °C under nitrogen atmosphere. The reaction mixture was stirred for 2 h at 25 °C and 2 h at 60 °C. The reaction mixture was carefully quenched with ice-cold water (1 mL) at 0 °C, and 10% NaOH (1 mL) was added. The resulting mixture was stirred for 10 min at room temperature, filtered through Celite, and washed with CH2Cl2 (25 mL). The resulting filtrate was dried over Na2SO4 and concentrated under reduced pressure and the crude material was purified by semipreparative reverse phase HPLC to obtain the compound 43 as a white solid (5 mg, 26%). 1H NMR (400 MHz, MeOD) δ 8.33 (s, 1H), 7.39 (s, 1H), 7.28 (s, 1H), 3.07 (t, J = 7.7 Hz, 2H), 2.94 (t, J = 7.6 Hz, 4H), 2.86–2.73 (m, 4H), 1.82–1.66 (m, 10H), 1.58–1.40 (m, 8H), 0.95 (t, J = 6.8 Hz, 3H). 13C NMR (126 MHz, MeOD) δ 154.80, 148.71, 141.75, 138.97, 136.98, 128.10, 125.79, 119.63, 115.24, 40.68, 40.68, 36.73, 32.74, 32.45, 32.12, 31.61, 30.84, 29.02, 28.52, 28.42, 27.37, 27.14, 23.63, 14.44. MS (ESI-TOF) for C24H40N4 [M + H]+ calculated 385.3326, found 385.3330.

Protein Expression, Purification, and Crystallization

The extracellular domain of human TLR8 (hTLR8, residues 27–827) was prepared as described previously[74] and was concentrated to 16 mg/mL in 10 mM MES (pH 5.5), 50 mM NaCl. The protein solutions for the crystallization of hTLR8/compound complexes contained hTLR8 (8.5 mg/mL) and compound (protein/compound molar ratio of 1:10) in a crystallization buffer containing 7 mM MES (pH 5.5), 35 mM NaCl. Crystallization experiments were performed with sitting-drop vapor-diffusion methods at 293 K. Crystals of hTLR8/compound were obtained with reservoir solutions containing 9–12% (w/v) PEG3350, 0.3 M potassium formate, and 0.1 M sodium citrate (pH 4.8–5.2).

Data Collection and Structure Determination

Diffraction data sets were collected on beamlines PF-AR NE3A (Ibaraki, Japan) and SPring-8 BL41XU under cryogenic conditions at 100 K. Crystals of hTLR8/compound were soaked into a cryoprotectant solution containing 15% (w/v) PEG3350, 0.23 M potassium formate, 75 mM sodium citrate, pH 4.8–5.2, 7.5 mM MES pH 5.5, 38 mM NaCl, and 25% glycerol. Data sets were processed using the HKL2000 package[75] or imosflm.[76] HTLR8/compound structures were determined by the molecular replacement method using the Molrep program[77] with the hTLR8/CL097 structure (PDB code 3W3J) as a search model. The model was further refined with stepwise cycles of manual model building using the COOT program[78] and restrained refinement using REFMAC[79] until the R factor was converged. Compound molecule, N-glycans, and water molecules were modeled into the electron density maps at the latter cycles of the refinement. The quality of the final structure was evaluated with PROCHECK.[80] The statistics of the data collection and refinement are also summarized in Table S1. The figures representing structures were prepared with PyMOL (Schrödinger, New York, NY). Coordinates have been deposited in the Protein Data Bank of the Research Collaboratory for Structural Bioinformatics; PDB codes for compounds 1 and 2 are, respectively, 5AWD and 5AWB.

Human TLR8-Specific Reporter Gene Assays (NF-κB Induction) and TLR-2, -3, -4, -5, -7, -9- and NOD-1/NOD-2 Counterscreens

The induction of NF-κB was quantified using human TLR-2, -3, -4, -5, -7, -8, -9, and NOD-1/NOD-2-specific, rapid-throughput, liquid handler-assisted reporter gene assays as previously described by us.[31,47,60,61] HEK293 cells stably co-transfected with the appropriate hTLR (or NOD) and secreted alkaline phosphatase (sAP) were maintained in HEK-Blue Selection medium. Stable expression of secreted alkaline phosphatase (sAP) under control of NF-κB/AP-1 promoters is inducible by appropriate TLR/NOD agonists, and extracellular sAP in the supernatant is proportional to NF-κB induction. Reporter cells were incubated at a density of ∼105 cells/ml in a volume of 80 μL/well, in 384-well, flat-bottomed, cell culture-treated microtiter plates in the presence of graded concentrations of stimuli. sAP was assayed spectrophotometrically using an alkaline phosphatase-specific chromogen (present in HEK-detection medium as supplied by InvivoGen) at 620 nm. None of the compounds were active in the counterscreens (data not shown), confirming specificity for human TLR8.

Immunoassays for Cytokines

Fresh human peripheral blood mononuclear cells (hPBMC) were isolated from human blood obtained by venipuncture with informed consent and as per institutional guidelines on Ficoll–Hypaque gradients. Aliquots of PBMCs (105 cells in 100 μL/well) were stimulated for 12 h with graded concentrations of test compounds. Supernatants were isolated by centrifugation and were assayed in duplicates using analyte-specific multiplexed cytokine/chemokine bead array assays as reported by us previously.[59]

Rabbit Immunization and CRM197[72]-Specific Immunoassays

All experiments were performed at Harlan Laboratories (Indianapolis, IN) in accordance with institutional guidelines. All antigen/adjuvant preparations were entirely aqueous; no liposomal or emulsifying agents were used. Cohorts of adult female New Zealand Wwhite rabbits (n = 4) were immunized intramuscularly in the flank region with (a) 10 μg of CRM197[72] in 0.2 mL of saline (unadjuvanted control) or (b) 10 μg of CRM197 in 0.2 mL of saline plus 100 μg of lead TLR8 agonists. Preimmune test-bleeds were first obtained via venipuncture of the marginal vein of the ear. Animals were immunized on days 1, 15, and 28. A final test-bleed was performed via the marginal vein of the ear on day 38. Sera were stored at −80 °C until used. CRM197-specific ELISAs were performed in 384-well format using automated liquid handling methods as described by us elsewhere.[52] A precision 2000 liquid handler (Bio-Tek, Winooski, VT) was used for all serial dilution and reagent addition steps, and a Bio-Tek ELx405 384-well plate washer was employed for plate washes; 100 mM phosphate-buffered saline (PBS), pH 7.4, containing 0.1% Tween-20 was used as wash buffer. Nunc-Immuno MaxiSorp (384-well) plates were coated with 30 mL of CRM197 (10 μg/mL) in 100 mM carbonate buffer, pH 9.0, overnight at 4 °C. After 3 washes, the plates were blocked with 3% bovine serum albumin (in PBS, pH 7.4) for 1 h at rt. Serum samples (in quadruplicate) were serially diluted in a separate 384-well plate using the liquid handler, and an amount of 30 μL of the serum dilutions was transferred using the liquid handler, and the plate was incubated at 37 °C for 2 h. The assay plate was washed three times, and 30 μL of 1:10 000 diluted appropriate anti-rabbit immunoglobulin (IgG, γ chain) conjugated with horseradish peroxidase was added to all wells. Following an incubation step at 37 °C for 1 h and three washes, tetramethylbenzidine substrate was added at concentrations recommended by vendor (Sigma). The chromogenic reaction was terminated at 30 min by the addition of 2 M H2SO4. Plates were then read at 450 nm using a SpectraMax M4 device (Molecular Devices, Sunnyvale, CA).

Eight-Color Flow-Cytometric Immunostimulation Experiments

Cell surface marker upregulation was determined by flow cytometry using protocols published by us previously[73] and modified for rapid throughput. Briefly, heparin-anticoagulated whole blood samples were obtained by venipuncture from healthy human volunteers with informed consent and as per guidelines approved by the University of Kansas Human Subjects Experimentation Committee. Serial dilutions of selected compounds were performed using a Bio-Tek Precision 2000 XS liquid handler in sterile 96-well polypropylene plates, to which were added 100 mL aliquots of anticoagulated whole human blood. The plates were incubated at 37 °C for 16 h. Negative (endotoxin free water) controls were included in each experiment. The following fluorochrome-conjugated antibodies were used: CD3-PE, CD19-FITC, CD56-APC (eBioscience, San Diego, CA), CD14-V500, CD28 PE-Cy7, CD40 V450, CD80 APC-H7, CD86 PerCP-Cy5.5 (Becton-Dickinson Biosciences, San Jose, CA). Following incubation, 2.5 μg of each antibody was added to wells with a liquid handler and incubated at 4 °C in the dark for 60 min. Following staining, erythrocytes were lysed and leukocytes fixed by mixing 200 mL of the samples in 800 mL prewarmed whole blood lyse/fix buffer (Becton-Dickinson Biosciences, San Jose, CA) in 96 deep-well plates. After washing the cells twice at 300 g for 10 min in RPMI, the cells were transferred to a 96-well plate. Flow cytometry was performed using a BD FACSVerse instrument for acquisition on 100 000 gated events. Compensation for spillover was computed for each experiment on singly stained Comp Beads (Becton-Dickinson Biosciences, San Jose, CA). CD28, CD40, CD80, and CD86 activation in the major leukocyte populations, viz., natural killer lymphocytes (NK cells CD3–CD56+), cytokine-induced killer phenotype (CIK cells CD3+CD56+), B lymphocytes (CD19+CD3–), T lymphocytes (CD3+CD56–), monocytes (CD14+), polymorphonuclear cells (CD14–) were quantified using FlowJo, version 7.0, software (Treestar, Ashland, OR).